Detection of human PD-1 on T-cells using a fusion protein consisting of an anti-PD-1 single chain variable fragment linked to superfolder GFP.

Monoclonal antibodies that disrupt the interaction between T-cell derived PD-1 and immunosuppressive ligands, such as PD-L1, have dramatically improved approaches to cancer therapy. One such antibody is termed Nivolumab (trade name Opdivo) that selectively targets PD-1. We previously described a Nivolumab-based anti-PD-1 single chain variable fragment (scFv), termed the anti-PD-1 double mutant (dm) scFv, that tightly binds to PD-1 and blocks the interaction between PD-1 expressed on T-cells and PD-L1 on CHO cells. Extending these experiments, we now report a fluorescent reporter formed by the fusion of the anti-PD-1dm with superfolder (sf) GFP. Immunofluorescence and flow cytometry studies established that the anti-PD-1dm-sfGFP fusion protein can be used to detect PD-1 on the surface of PD-1 expressing Jurkat cells. Furthermore, using a humanized mouse strain that expresses human PD-1 and PD-L1, we report that when combined with an anti-CD3 antibody, the anti-PD-1dm-sfGFP can be used to identify PD-1 expressing T-cells within mouse tumor biopsies. Thus, we have developed a reagent for the quantitative determination of activated T-cells in tumor biopsies. Finally, we report that an additional fluorescent probe for the detection of PD-1 in vivo can be generated by linking, via maleimide chemistry, a derivative of the anti-PD-1dm to the near-infrared dye IR800.